FIG. 1 illustrates a typical CD-ROM disc drive 12 and personal computer 40. CD-ROM disc drive 12 reads data stored on a compact disc 14. A number of standards govern the manufacture of compact disc 14. The first standard introduced, the Compact Disc Digital Audio Standard, commonly referred to as the Red Book, defined a single type of track, audio. Subsequently, the CD-ROM Standard, known as the Yellow Book, further defined the Red Book by adding two additional types of tracks: CD-ROM Mode 1, for computer data, and CD-ROM Mode 2, for compressed audio data and video picture data.
According to the standards of the Red and Yellow Books, the recorded area of compact disc 14 is divided into three parts: lead-in area 15, program area 16, and lead-out area 17. Program area 16 is divided into tracks and may include as many as 99. A track may be thought of as a partition of CD-ROM address space. Tracks have a minimum length of 300 sectors. Multi-session CD-ROM discs include multiple sessions, each recorded at a different time and having its own lead-in, program and lead-out area.
Information stored on compact disc 14 is organized into sectors. Each sector includes 2352 bytes of information and 98 bytes of control data. The eight bits of a control byte are individually named according to the which sub-channel they represent: P, Q, R, S, T, U, V and W. Thus, all the second bits of each control byte represent the Q sub-channel, which contains the running times from the beginning of the disc and from the beginning of the current track. The Q sub-channel of lead-in area 15 is used to store information about the CD-ROM type and lay-out, information referred to as the disc's table of contents. This table of contents is continuously repeated throughout the lead-in area, with each TOC item of information repeated three times. TOC integrity requires that the assembled TOC include all TOC items, no items repeated and all items presented in their correct order.
Table I of FIG. 2 illustrates the various data formats that may be used to describe lead-in Sub-channel Q data. Within the Control/ADR byte the four bit ADR field defines the item mode, which indicates which other fields in the item are meaningful. Table II of FIG. 3 is an example of a TOC.
According to current standards a CD-ROM disc drive must assemble and store the TOC because the lead-in area, by definition, is not accessible to personal computers. Thus, to support TOC assembly CD-ROM disc drive 12 includes microcontroller 20 and memory 22. Memory 22 not only stores TOC 26, but also instructions for creating the TOC, referred to as TOC Driver 24. Under the direction of TOC Driver 24, microcontroller 20 responds to the presence of a new CD-ROM by reading the lead-in Sub-Channel Q data via Read Circuitry 18 and creating a new TOC 26, which is then stored in memory 22.
Creation of TOC 26 by CD-ROM disc drive 12 allows personal computer 40 to identify and locate the information on CD-ROM 16 by simply issuing a read command. Instructions for READ TOC command 42 form part of the disc driver instructions 44 stored within memory 45. When issued by central processing unit (CPU) 46, the signals representing the READ TOC command are conveyed via input/output (I/O) interface 47 and a I/O bus 48 to CD-ROM disc drive 12.
A disadvantage of the prior personal computer system is the computational and financial cost of disc drive based TOC assembly. Microcontroller 20 must be more sophisticated, and thus more expensive, than if TOC construction were not CD-ROM disc drive based. Similarly, the total capacity of memory 22 must be greater, and thus more expensive, than would be the case if CD-ROM disc drive 12 did not store the TOC.